Light spot shaping device and method,light pickup device, and optical disk apparatus

ABSTRACT

A laser beam for reproduction emitted from an LD (41) at the time of reproduction passes through an As correction board (42) and a grating (43) and becomes incident on a beam splitter (44). The beam splitter (44) transmits the laser beam and causes the laser beam to be incident on a liquid crystal unit (45). Then, at the time of reproduction, a light spot shaping device provides aberration to the laser beam transmitted through the liquid crystal unit (45) in accordance with the type of a magneto-optical disc and thus shapes a light spot on the magneto-optical disc. Therefore, optimum light spots for different media can be shaped.

TECHNICAL FIELD

[0001] This invention relates to a light spot shaping device and methodfor shaping a spot of light cast onto a medium, an optical pickup deviceadapted to at least a plurality of types of removable optical discshaving different track pitches and for forming a spot of light on anoptical disc and reproducing an information signal, and an optical discdevice.

BACKGROUND ART

[0002] Optical discs having a small diameter of approximately 64 mm andhaving a storage capacity which enables recording of, for example, notless than 74 minutes of music signals, have been broadly known. Thesesmall-diameter optical discs are called mini disc MD (trade name, SonyCorporation). Such discs are classified into two types, that is,reproduction-only type discs on which data is recorded in the form ofpits, and recording/reproduction type discs on which data is recorded bythe magneto-optical (MO) recording system and can also be reproduced.The following description relates to the recording/reproduction type(herein after referred to as magneto-optical disc).

[0003] With respect to magneto-optical discs, the track pitch, therecording wavelength of a recording laser beam, or NA of an objectivelens has been improved in order to increase the recording capacity.

[0004] An initial magneto-optical disc for groove recording at a trackpitch of 1.6 μm and the EFM modulation system is referred to asfirst-format magneto-optical disc. A second-generation magneto-opticaldisc for land recording at a track pitch of 0.95 μm and the RLL (1, 7)modulation system is referred to as second-format magneto-optical disc.A third-generation magneto-optical disc for land and groove recording ata track pitch of 0.70 μm or less and the RLL (1, 7) modulation system isreferred to as a third-format magneto-optical disc.

[0005]FIG. 17 shows the specifications of these three types ofmagneto-optical discs. The remarkable improvement in the recordingcapacity from 140 MB of the first-format magneto-optical disc to 650 MBof the second-format magneto-optical disc and to 2 GB of thethird-format magneto-optical disc is due to the continuous narrowing ofthe track pitch as described above and the reduction in the pit length.It is also due to the development of techniques related to therespective specifications as shown in FIG. 17.

[0006] Referring to FIG. 18, which shows the address format of eachmagneto-optical disc, how the third-format magneto-optical disc hasacquired the above-described recording capacity will now be described.FIGS. 18A, 18B and 18C illustrate the address formats of thefirst-format magneto-optical disc, the second-format magneto-opticaldisc and the third-format magneto-optical disc, respectively. Thefirst-format magneto-optical disc has an address format which employsgroove recording at a track pitch of 1.6 μm and single-spiraldouble-sided wobbling. The second-format magneto-optical disc has anaddress format which employs land recording at a track pitch of 0.95 μmand double-spiral one-sided wobbling. The third-format magneto-opticaldisc has an address format which employs land and groove recording at atrack pitch of 0.70 μm or less and double-spiral one-sided wobbling.

[0007] Particularly in the third-format magneto-optical disc, the trackpitch is narrowed to 0.70 μm or less, as described above. In theordinary groove recording system or land recording system, the trackpitch is too narrow to a spot of laser beam and therefore causes atracking error to be small. In the third-format magneto-optical disc,however, since the land and groove recording system is employed, thegroove pitch is 1.4 μm or less, which is double the track pitch, and alarger tracking error signal can be taken than in the conventionalsecond-format magneto-optical disc. The address input method of thethird-format magneto-optical disc is one-sided wobbling, similarly tothe second-format magneto-optical disc, and the absolute address isencoded in this wobbling by FM modulation and biphasic modulation. Theformat of the address is the same as that of the second-formatmagneto-optical disc. What is different is that in the second-formatmagneto-optical disc, a groove itself is wobbled to enter addressinformation, as shown in FIG. 18B, whereas in the third-formatmagneto-optical disc, only one side of a groove is wobbled and the otherside is kept as DC, as shown in FIG. 18C. By employing this system, itis possible to narrow the track pitch while restraining the cross talkbetween adjacent wobbles.

[0008] The most outstanding feature of the third-format magneto-opticaldisc is data reproduction based on domain wall displacement detection(DWDD). As domain wall displacement is used, lower compatibility ismaintained by having a laser wavelength of 650 mm and a lens numericalaperture of 0.52, which are the same as those of the optical system forthe second-format magneto-optical disc, despite a high linear densityapproximately 2.6 times that of the second-format magneto-optical disc.

[0009] The third-format magneto-optical disc employs the RLL (1, 7)modulation system for recording signals, similarly to the second-formatmagneto-optical disc, but it uses LDC (long distance code) with BIS(burst indicator subcode) of high correction performance as an errorcorrecting code. The minimum recording unit is 64 kilobytes. As a resultof the above, a recording capacity of 2 GB can be achieved, which isapproximately 3.1 times the recording capacity of 650 MB of thesecond-format magneto-optical disc.

[0010] Meanwhile, it is difficult to read signals recorded on theabove-described magneto-optical discs of the three generations whilerealizing compatibility on an optical pickup device having fixed opticalconditions.

[0011] On the first-format magneto-optical disc, which has a relativelywide track pitch, address information is recorded as an ADIP (address inpregroove) signal based on double-sided wobbling of the groove andtherefore a somewhat large spot is necessary. As for the second-formatmagneto-optical disc, for which a laser beam with a short wavelength of650 nm and an objective lens with NA of 0.52 are used, a narrow skewmargin is further reduced by changing the numerical aperture of theoptical pickup. With respect to the third-format magneto-optical disc,on which a signal is reproduced using the above-described DWDD, thedomain wall displacement characteristic is changed by the spot shape atthe time of reproduction and a spot which is small in the radialdirection is suitable for improving the crosslight characteristic at thetime of recording.

[0012] In this manner, there are optimum spot shapes for these discs,respectively. Therefore, it is difficult to realize compatibility on anoptical pickup device having fixed optical conditions.

[0013] Moreover, in an optical disc device, as a magneto-optical signalrecording/reproducing device having a reproducing unit for reproducing asignal recorded on a optical disc at a high density, for example, by theabove-described DWDD, it is difficult to cast a laser beam forrecording/reproduction onto the optical disc by using only one opticalpickup device. Since DWDD utilizes the temperature distribution on themedium at the time of reproduction, the optimum profile for the laserbeam differs between recording and reproduction and therefore itsperformance cannot be sufficiently exerted.

DISCLOSURE OF THE INVENTION

[0014] In view of the foregoing status of the alt it is an object of thepresent invention to provide a light spot shaping device and method, anoptical pickup device and an optical disc device which enable shaping ofan optimum light spot to a plurality of different media.

[0015] It is another object of the present invention to provide a lightspot shaping device and method, an optical pickup device and an opticaldisc device which enables casting of a recording and/or reproducinglaser beam onto an optical disc from a single optical pickup devicewhile changing the shape of its spot.

[0016] A light spot shaping device according to the present invention isadapted for shaping a spot of light cast onto a plurality of types ofremovable media from the same light source through the same opticalpath, in accordance with the type of the medium. The device comprises:liquid crystal means having a split pattern electrode formed along thedirection of a recording track of the medium; and control means forchanging a voltage to be applied to the split pattern electrode of theliquid crystal means in accordance with the type of the medium and thuschanging the optical characteristic of the light spot.

[0017] In this light spot shaping device, the control means changes thevoltage to be applied to the split pattern electrode of the liquidcrystal means in accordance with the type of the medium, therebyproviding aberration to the light at least along the direction of thetrack so as to shape the light spot.

[0018] A light spot shaping method according to the present invention isadapted for shaping a spot of light cast onto a plurality of types ofremovable media from the same light source through the same opticalpath, in accordance with the type of the medium. The method comprises acontrol step of providing liquid crystal means having a split patternelectrode formed along the direction of a recording track of the mediumand changing a voltage to be applied to the split pattern electrode ofthe liquid crystal means in accordance with the type of the medium, thuschanging the optical characteristic of the light spot.

[0019] In this light spot shaping method, at the control step, thevoltage to be applied to the split pattern electrode of the liquidcrystal means is changed in accordance with the type of the medium,thereby providing aberration to the light at least along the directionof the track so as to shape the light spot on the medium.

[0020] A light spot shaping device according to the present invention isadapted for separately shaping an incident laser beam in recording andin reproduction to a spot of light cast onto a medium for recordingand/or reproducing an information signal. The device comprises: liquidcrystal means having a split pattern electrode formed along thedirection of a recording track of the medium; ad control means forchanging a voltage to be applied to the split pattern electrode of theliquid crystal means between the recording and the reproduction and thuschanging the optical characteristic of the light spot.

[0021] In this light spot shaping device, the control means changes thevoltage to be applied to the split pattern electrode in a reproductionmode for reproducing the information signal from the medium, thusproviding aberration to the light incident on the liquid crystal meansalong the direction of the recording track of the medium so as to shapethe light spot on the medium.

[0022] A light spot shaping method according to the present invention isadapted for separately shaping an incident laser beam in recording andin reproduction to a spot of light cast onto a medium for recordingand/or reproducing an information signal. The method comprises a controlstep of providing liquid crystal means having a split pattern electrodeformed along the direction of a recording track of the medium andchanging a voltage to be applied to the split pattern electrode of theliquid crystal means between the recording and the reproduction, thuschanging the optical characteristic of the light spot.

[0023] In this light spot shaping method, at the control step, thevoltage to be applied to the split pattern electrode is changed in areproduction mode for reproducing the information signal from themedium, thus providing aberration to the light incident on the liquidcrystal means along the direction of the recording track of the mediumso as to shape the light spot on the medium.

[0024] An optical pickup device according to the present invention isadapted for forming a spot of light adapted to a plurality of types ofremovable optical discs having at least different track pitches, ontothe optical disc, thus reading an information signal. The devicecomprises: a light source for emitting light; an optical system forcasting the light emitted from the light source onto a signal recordingsurface of the optical disc and passing return light reflected by thesignal recording surface of the optical disc; photodetection means fordetecting the return light passed by the optical system; liquid crystalmeans provided in the optical system and having a split patternelectrode stacked in a radial direction of the optical disc; and lightspot shaping means for changing a voltage to be applied to the splitpattern electrode of the liquid crystal means for each type of theoptical disc and thus changing the optical characteristic of the lightspot.

[0025] In this optical pickup device, the light spot shaping meanschanges the voltage to be applied to the split pattern electrode of theliquid crystal means in accordance with the type of the optical disc,thus providing aberration to the light at least along the radialdirection so as to shape the light spot.

[0026] An optical pickup device according to the present invention isadapted for casting recording light and/or reproducing light forrecording and/or reproducing an information signal to an optical disc.The device comprises: a light source for emitting light; an opticalsystem for casting the light emitted from the light source onto a signalrecording surface of the optical disc and passing return light reflectedby the signal recording surface of the optical disc; photodetectionmeans for detecting the return light passed by the optical system;liquid crystal means provided in the optical system and having a splitpattern electrode stacked in a radial direction of the optical disc; andlight spot shaping means for changing the optical characteristic of thelight spot between when casting the recording light and when casting thereproducing light.

[0027] In this optical pickup device, the light spot shaping meanschanges the voltage to be applied to the split pattern electrode of theliquid crystal means in a reproduction mode for reproducing theinformation signal from the optical disc, thus providing aberration tothe light incident on the liquid crystal means along a tangentialdirection of a track of the optical disc so as to shape the light spoton the optical disc.

[0028] An optical disc device according to the present invention havinga reproducing part for forming a spot of light adapted to a plurality oftypes of removable optical discs having at least different trackpitches, onto the optical disc, thus reading an information signal fromeach optical disc. In the optical disc device, the reproducing partcomprises: a light source for emitting light; an optical system forcasting the light emitted from the light source onto a signal recordingsurface of the optical disc and passing return light reflected by thesignal recording surface of the optical disc; photodetection means fordetecting the return light passed by the optical system; liquid crystalmeans provided in the optical system and having a split patternelectrode stacked in a radial direction of the optical disc; and lightspot shaping means for changing a voltage to be applied to the splitpattern electrode of the liquid crystal means in accordance with thetype of the optical disc and thus changing the optical characteristic ofthe light spot so as to shape the light spot. In the optical discdevice, the information signal is reproduced on the basis of thequantity of the return light detected by the photodetection means.

[0029] In this optical disc device, the light spot shaping means changesthe voltage to be applied to the split pattern electrode of the liquidcrystal means in accordance with the type of the optical disc, thusproviding aberration to the light at least along the radial direction soas to shape the light spot on the optical disc.

[0030] An optical disc device according to the present invention isadapted for casting recording light and/or reproducing light to anoptical disc so as to record and/or reproduce an information signal. Thedevice comprises: a light source for emitting light; an optical systemfor casting the light emitted from the light source onto a signalrecording surface of the optical disc and passing return light reflectedby the signal recording surface of the optical disc; photodetectionmeans for detecting the return light passed by the optical system;liquid crystal means provided in the optical system and having a splitpattern electrode stacked in a radial direction of the optical disc; andlight spot shaping means for changing the optical characteristic of thelight spot between when casting the recording light and when casting thereproducing light.

[0031] In this optical disc device, the light spot shaping means changesthe voltage to be applied to the split pattern electrode of the liquidcrystal means in a reproduction mode for reproducing the informationsignal from the optical disc, thus providing aberration to the lightincident on the liquid crystal means along a tangential direction of atrack of the optical disc so as to shape the light spot on the opticaldisc.

[0032] The other objects and advantages of the present invention will befurther clarified by the following description of embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a block diagram showing the structure of amagneto-optical disc recording/reproducing device as a first embodiment.

[0034]FIG. 2 shows the structure of an optical pickup device provided inthe magneto-optical disc recording/reproducing device shown in FIG. 1.

[0035]FIG. 3 shows a split pattern electrode of a liquid crystal part ofa light spot shaping device provided in the magneto-optical discrecording/reproducing device shown in FIG. 1.

[0036]FIG. 4 is a graph showing light intensity distribution on asecond-format magneto-optical disc when the disc is inclined 0.7 degrees(radial skew).

[0037]FIG. 5 schematically illustrates spot shaping carried out by thelight spot shaping device shown iii FIG. 3.

[0038]FIG. 6 shows an applied voltage for acquiring a light spot for athird-format magneto-optical disc by shaping from a light spot for thesecond-format magneto-optical disc with no liquid crystal correction.

[0039]FIG. 7 shows an applied voltage for providing a beam with anaberration pattern close to coma in the case of reproducing a signalfrom the second-format magneto-optical disc.

[0040]FIG. 8 shows a change characteristic of a spot size by providing alight spot with a defocus in a linear direction.

[0041]FIG. 9 is a block diagram showing the structure of a video camerarecording/reproducing device to which the magneto-optical discrecording/reproducing device shown in FIG. 1 is applied.

[0042]FIG. 10 is a block diagram showing the structure of amagneto-optical disc recording/reproducing device as a secondembodiment.

[0043]FIG. 11 schematically illustrate domain wall displacementdetection.

[0044]FIG. 12 is a graph for explaining the operation of themagneto-optical disc recording/reproducing device shown in FIG. 10.

[0045]FIG. 13 illustrates a ghost generated by domain wall displacementdetection.

[0046]FIG. 14 shows an actual temperature profile of a spot on amagneto-optical disc due to casting of a light beam.

[0047]FIG. 15 shows a ghost signal generated together with a data signalwhen reproducing a recorded signal from a magneto-optical disc (DWDD).

[0048]FIG. 16 shows elimination of a ghost signal when reproducing arecorded signal from a magneto-optical disc (DWDD).

[0049]FIG. 17 shows the specifications of three types of magneto-opticaldiscs.

[0050]FIG. 18 shows address formats of the respective magneto-opticaldiscs so as to explain how a third-format magneto-optical disc hasacquired its recording capacity.

BEST MODE FOR CARRYING OUT THE INVENTION

[0051] Hereinafter, embodiments of the present invention will bedescribed with reference to the drawings. A first embodiment will bedescribed first. This first embodiment is a magneto-optical discrecording/reproducing device which has a reproducing unit for forming alight spot adapted to each of three types of magneto-optical discshaving at least different track pitches, that is, the first-formatmagneto-optical disc, the second-format magneto-optical disc and thethird-format magneto-optical disc shown in FIG. 17, and reproducing aninformation signal from each magneto-optical disc, and a recording unitfor recording an information signal to each magneto-optical disc.

[0052] This magneto-optical disc recording/reproducing device has anoptical pickup device tot which a specific example of the light spotshaping device of the present invention is applied. The optical pickupdevice will be later described in detail.

[0053] First, referring to FIG. 1, a structure for rotating onemagneto-optical disc 1 of the three types of magneto-optical discsloaded on the magneto-optical disc recording/reproducing device, and astructure for moving an optical pickup device 4 over the magneto-opticaldisc 1 will be described. The magneto-optical disc 1 is rotated at apredetermined number of rotations by a spindle motor 2. The spindlemotor 2 is driven by a driver 3. The driver 3 is controlled by a digitalservo processor (DSSP) 23, which will be described later, thus rotatingthe spindle motor 2.

[0054] The magneto-optical disc 1 rotated by the spindle motor 2 isirradiated with a laser beam from the optical pickup device 4. Data onthe magneto-optical disc 1 is read by moving the optical pickup device 4in a radial direction of the magneto-optical disc 1. The optical pickupdevice 4 is supported by a thread mechanism having a thread motor 5 andis thus made movable in the radial direction of the magneto-optical disc1. A large shift of the reading position is made by this threadmechanism. As all objective lens, which will be described later, of theoptical pickup device 4 is supported by a biaxial driving circuit and ismoved in the radial direction of the magneto-optical disc 1 by thedriver 3 on the basis of a tracking servo operation, a small shift ofthe reading position is made. Moreover, as the objective lens is movedin directions toward and away from the magneto-optical disc 1 by thebiaxial driving circuit on the basis of a focusing servo operation, thefocusing of the laser beam on the signal recording surface of themagneto-optical disc 1 is controlled.

[0055] The structure of the reproducing unit will now be described. Theoptical pickup device 4 generates an RF signal and supplies the RFsignal to an RF amplifier 6. The signal amplified with a predeterminedgain by the RF amplifier 6 is sequentially supplied to an A/D converter7, an automatic gain control (AGC) circuit 8; an equalizer (EQ) anddigital PLL unit 9, a decoder 10 and a demodulator 11, which form asignal processing unit. The demodulator 11 is connected to a memory unit13, an ECC encoder/decoder 14 and a descrambler and decoder 15 via aninternal bus 12.

[0056] This reproducing unit operates as follows. Specifically, a signalpicked up from the magneto-optical disc 1 by the optical pickup device 4is photoelectrically converted in the optical pickup device 4 and theoutputted as an RF signal. This RF signal is inputted to the RFamplifier 6, amplified there with a predetermined gain and then suppliedto the A/D converter 7 constituting the signal processing unit. The RFsignal supplied to the A/D converter 7 is quantized. After that, thegain is controlled by the AGC processing unit 8, and then waveformshaping and generation of a sampling clock are carried out by theequalizer (EQ) and digital PLL unit 9. The resulting signal is decodedby the decoder 10 and then demodulated by the demodulator 11. While AGC,equalization and DPLL are performed on the A/D-converted RF sisal inthis case, analog AGC, equalization and PLL may be performed on thesignal before A/D conversion. The data stream demodulated by thedemodulator 11 is expanded on the memory 13 and each error connectingblock thereof is error-connected by the ECC encoder/decoder 14.Descrambling processing and decoding processing are performed on theerror-corrected data by the descrambler and decoder 15, and a DAT1signal is outputted togther with a transfer clock SCLK from a clockgenerator 16.

[0057] The structure of the recording unit will now be described. Aninputted signal DAT0 is processed by a scrambler and encoder 17 and thensequentially supplied to the memory unit 13, the ECC encoder/decoder 14and a modulator 18 via the internal bus 12. The modulator 18 suppliesmodulated data to a magnetic head driving unit 19. The magnetic headdriving unit 19 drives a magnetic head 20. The modulator 18 alsosupplies a clock signal to a laser APC circuit and driver 21.

[0058] The recording unit operates as follows. Specifically, scramblingprocessing and encoding processing by the scrambler and encoder 17 areperformed oil a signal DAT0 inputted synchronously with a transfer clockSCLK, which is then written into the memory unit 13. An error connectingparity is added to the data written in the memory unit 13 by the ECCencoder/decoder 14 and the resulting data is supplied to the modulator18 via the internal bus 12. The data modulated by the modulator 18 issupplied to the magnetic head 20 via the magnetic head driving unit 19.Meanwhile, a laser strobe modulation clock is supplied to the laser APCcircuit and driver 21 from the modulator 18.

[0059] The structure of a servo system will now be described. This servosystem has the following elements: a matrix amplifier 22 for extractinga servo en-or signal and a wobble signal, which will be described later,from a signal generated by the optical pickup device 4; a DSSP 23 forperforming predetermined servo processing on the thread mechanism andthe actuator of the optical pickup device 4 via the driver 3 on thebasis of the servo error signal and for performing spindle servoprocessing on the spindle motor (SM) 2 in accordance with a CLV controlsignal, which will be described later; and a system controller 27 forcontrolling the DSSP 23. The servo system also has a band pass filter(BPF) 24 for detecting an ADIP (address in pregroove) signal from thewobble signal extracted by the matrix amplifier, an ADIP decoder 25 fordecoding the ADIP signal, and a CLV control unit 26 for supplying a CLVcontrol signal to the DSSP 23.

[0060] The operation of the servo system will now be described. Phasecompensation, and gain and target value setting processing by the DSSP23 are performed on a servo error signal extracted by the matrixamplifier 22 from a signal from the optical pickup device 4, and theresulting signal is supplied to the actuator in the optical pickupdevice 4 and the thread motor 5 via the driver 3. Since a tracking errorsignal has opposite polarities at a land part and a groove part of themagneto-optical disc, the system controller 27 switches the polarity,depending on which part is to be recorded/reproduced. Particularly, itis known that when an astigmatic method is used for focus detection onthe land/groove disc, an offset between a land pall and a groove part isgenerated. To eliminate its influence, the system controller 27 sets afocusing offset separately at the land pail and at the groove part.

[0061] Meanwhile, a wobble signal outputted from the matrix amplifier 22has its component extracted by the band pass filter (BPF) 24, andaddress information decoded by the ADIP decoder 25 is transferred to thesystem controller 27. All integral of the output of the BPF 24 and thePLL phase error in the ADIP decoder 25, and a control signal from thesystem controller 27 are supplied to the CLV control unit 26 and aresupplied to the spindle motor 2 via the DSSP 23 and the driver 3.

[0062] The magneto-optical disc recording/reproducing device shown inFIG. 1 is adapted for recording and reproducing information signals toand from the first-format magneto-optical disc, the second-formatmagneto-optical disc and the third-format magneto-optical disc whichhave different specifications from one another. Therefore, the opticalpickup device 4 or the recording unit and the reproducing unit can beadapted to any of these discs.

[0063] The discrimination of the three types of discs is carried out byreading all identification mark provided on a cartridge, since all ofthese discs are housed in cartridges. The disc type may also bediscriminated by detecting the difference in format itself.

[0064] First, shaping of a light spot adapted to the three types ofmagneto-optical discs in the optical pickup device 4 as an essentialpart of the present invention will be described.

[0065]FIG. 2 shows the detailed structure of the optical pickup device4. Specifically, this optical pickup device 4 has a laser diode (LD) 41as a light source for emitting a laser beam, an irradiation path forirradiating the signal recording surface of the magneto-optical disc 1with the laser beam emitted from the LD 41, an optical system forforming a return light path which passes return light reflected by thesignal recording surface of the magneto-optical disc, and aphotodetector (PD) 51 for detecting the quantity of return light lead bythe return light path of the optical system. The optical system includesan As correction board 42, a grating 43, a beam splitter 44, acollimating lens 46, a mirror 47, an objective lens 48, a Wollastonprism 49, and a multi-lens 50. The optical pickup device 4 also has aliquid crystal unit 45 of a light spot shaping device as a specificexample of the light spot shaping device of the present invention,between the beam splitter 44 and the collimating lens 46 of the opticalsystem.

[0066] This light spot shaping device, at the time of reproduction,changes a voltage to be applied to a split pattern electrode of theliquid crystal unit 45 by a control unit in accordance with the type ofthe magneto-optical disc 1, thereby changing the optical characteristicof the light spot so as to shape the light spot.

[0067] In the following description, it is assumed that the opticalpickup device 4 is designed for the second-format magneto-optical disc,for example. In the optical pickup device 4, a reproducing laser beamemitted from the LD 41 at the time of reproduction passes through the Ascorrection board 42 and the grating 43 and becomes incident on the beamsplitter 44. The beam splitter 44 passes the laser beam and causes thelaser beam to be incident on the liquid crystal unit 45. At the time ofreproduction, the light spot shaping device provides aberration to thelaser beam passing through the liquid crystal unit 45 in accordance withthe type of the magneto-optical disc and thus shapes the light spot onthe magneto-optical disc. As will be later described in detail, bychanging a voltage to be applied to split pattern electrodes A, B, C, Dand E of the liquid crystal unit 45 as shown in FIG. 3, the laser beamis provided with aberration and the light spot on the magneto-opticaldisc is shaped in a radial direction or in a linear direction. The laserbeam shaped in accordance with each magneto-optical disc by the liquidcrystal unit 45 of the light spot shaping device is collimated by thecollimating lens 46 and reflected by the mirror 47. After that, thelaser beam is condensed by the objective lens 48 and cast onto thesignal recording surface of the magneto-optical disc 1.

[0068] Return light reflected by the signal recording surface of themagneto-optical disc 1 passes through the objective lens 48, the mirror47, the collimating lens 46 and the liquid crystal unit 45, and thenreflected to the direction of the PD 51 by the beam splitter 44. Thereturn light is then split by the Wollaston prism 49, condensed by themulti-lens 50 and made incident on a light receiving surface oil the PD51.

[0069] On the PD 51, a plurality of quadrisected light receivingsurfaces each having a quadrisected light receiving area, for example,two quadrisected light receiving surfaces are provided, and a receivedlight quantity signal (RF signal) detected by the PD 51 is supplied tothe RF amplifier 6 shown in FIG. 1.

[0070] The liquid crystal unit 45 of the light spot shaping device isformed in a circular or elliptical shape having the split patternelectrodes A, B, C, D and E as shown ill FIG. 3 along the radialdirection of the magneto-optical disc 1. For example, with the center ofthe circle assumed as 0, the pattern electrodes A, B, C, D and E havethe following widths in the radial direction: A=−1.0 to −0.85; B=−0.85to −0.13; C=−0.13 to +0.13; D=+0.13 to +0.85; and E=+0.85 to +1.00.

[0071] Since the optical pickup device 4 is designed for thesecond-format magneto-optical disc as described above, the wavelength λof the laser beam is 650 nm and the numerical aperture NA of theobjective lens 48 is 0.52, as shown in FIG. 17.

[0072] In the case of reproducing data from the first-formatmagneto-optical disc by using such an optical pickup device 4, the spotfor the second-format magneto-optical disc, which is small in the radialdirection, must be increased by defocusing to a certain extent in orderto read ADIP, because address information is recorded on thefirst-format magneto-optical disc by using an ADIP signal based oildouble-sided wobbling of the groove as described with reference to FIG.18. However, too much defocusing reaches the end of an S shape of focuslead-in and consequently no defocusing margin can be taken. To overcomethis, the light spot shaping device provides aberration to the spot forthe second-format magneto-optical disc and carries out spot shaping sothat the spot is laterally elongated in the radial direction.

[0073] In the case of reproducing data from the third-formatmagneto-optical disc by using the optical pickup device 4, since arecorded signal via a domain wall enlarged in the linear direction isdetected on the third-format magneto-optical disc by DWDD, a verticallylong spot in the linear direction increases the light quantitycontributing to the reproduction. Therefore, the reproductioncharacteristic is unproved and the crosslight characteristic inrecording is improved. Thus, the light spot shaping device providesaberration to the spot for the second-format magneto-optical disc andcarries out spot shaping so that the spot is vertically elongated in thelinear direction. Moreover, defocusing is carried out as will bedescribed later.

[0074] In the case of reproducing data from the second-formatmagneto-optical disc, as an aberration pattern close to coma is providedto the beam by the light spot shaping device and coma correction basedon the skew is carried out in order to enlarge a radial skew margin thereproduction characteristic can be improved. For example, a lightintensity distribution characteristic on the disc when the second-formatmagneto-optical disc is inclined 0.7 degrees (radial skew) is shown by abroken line in FIG. 4. If the intensity at the center of the spot is 1,the intensity is once lowered to 0 around a position away from thecenter by +0.7 μm and then raised to an intensity peak of 0.05 at aposition of +1 μm to form a convex shape. The light intensitydistribution characteristic shown by the broken line exhibits a spreadbottom as a whole. Therefore, according to the light intensitydistribution characteristic shown by the broken line, it is known thatan adjacent track may be read because of the radial skew of 0.7 degrees.Thus, the light spot shaping device carries out liquid crystalcorrection so as to eliminate the convex shape having the intensity peakof 0.05 and to prevent the spreading of the bottom on both sides. InFIG. 4, the light intensity distribution characteristic after the liquidcrystal correction by the light spot shaping device is shown by a solidline. According to the light intensity distribution characteristic ofthis solid line, since any deviation of the light spot from the lateraltrack is eliminated, the reproduction characteristic can be improved.

[0075] Referring to FIGS. 5 to 8, the operation of the light spotshaping device to shape a light spot for the second-formatmagneto-optical disc in accordance with the three types ofmagneto-optical discs by light spot shaping using the liquid crystalunit 45 will now be described.

[0076]FIG. 5 is a view for schematically showing spot shaping.

[0077] First, the operation of the light spot shaping device to shape alight spot for the first-format magneto-optical disc from a light spotfor the second-format magneto-optical disc with no liquid crystalcorrection will be described. In this case, the light spot shapingdevice supplies an applied voltage as shown in FIG. 6 to the splitelectrode pattern parts A and E of the liquid crystal unit 45 shown inFIG. 3 and provides an aberration pattern close to astigmatism to abeam. Thus, a spot which is elongate in a radial direction (rad) can beshaped.

[0078] Although not shown in FIG. 5, the operation to provide anaberration pattern close to coma to a beam and carry out coma correctionbased on skew in the case of reproducing data from the second-formatmagneto-optical disc will be described. In the light spot shapingdevice, voltages of different magnitudes in one direction (A>D) areapplied to the split electrode pattern parts A and D of the liquidcrystal unit 45 and voltages of different magnitudes in the otherdirection (E>B) are applied to the pairs B and E, as shown in FIG. 7.Thus, an aberration pattern close to coma is provided to a beam and comacorrection based on skew is carried out to enlarge a radial skew margin.

[0079] The operation of the light spot shaping device to acquire, byshaping, a light spot for the third-format magneto-optical disc from alight spot from the second-format magneto-optical disc with no liquidcrystal correction will now be described. In this case, the light spotshaping device supplies an applied voltage as shown in FIG. 6 to thesplit electrode pattern parts A and E of the liquid crystal unit 45shown in FIG. 3, then provides an aberration pattern close toastigmatism to a beam, and provides a defocus in a tangential direction(tan), thus shaping a spot which is elongate in the tangentialdirection. FIG. 8 shows a change characteristic of a spot size byproviding a defocus in the tangential direction to a light spot. Thelight intensity 1/e² and ½ used for defining the spot size on the discare used as parameters in the tangential direction (tan) and the radialdirection (rad), respectively. It is understood that when the lightintensity is 1/e², the defocus becomes close to 2 μm and that the spotsize rapidly increases as the defocus exceeds 2 μm. Therefore, byproviding a defocus of approximately 2 μm to the light for thesecond-format magneto-optical disc, a light spot for the third-formatmagneto-optical disc which is elongate in the tangential direction canbe shaped.

[0080] As described above, in the magneto-optical discrecording/reproducing device shown in FIG. 1, at the time ofreproduction, an optimum spot for each disc can be shaped simply bychanging an applied voltage pattern to be applied to the liquid crystalunit 45 in accordance with each of the three types of magneto-opticaldiscs by the light spot shaping device in the optical pickup device 4.Therefore, the compatibility can be secured inexpensively and with asimple structure.

[0081] As described above, in this magneto-optical discrecording/reproducing device, the recording unit and the reproducingunit as well as the optical pickup device 4 can be adapted to recordingto and reproduction from the three types of magneto-optical discs.

[0082] First, in the recording unit, the ECC encoder/decoder 14 adds anerror correcting code to data written in the memory 13. In this case,ACIRC (advanced cross interleave Reed-Solomon code) processing isperformed on data for the first-format magneto-optical disc. RS-PC(Reed-Solomon parallel code) processing is performed on data for thesecond-format magneto-optical disc. RS-LDC (Reed-Solomon long distancecode) processing performed on data for the third-format magneto-opticaldisc.

[0083] The modulator 18 performs modulation processing corresponding toeach type of disc on the data on which the above-described respectiveECC processing has been performed by the ECC encoder/decoder 14. EFMprocessing is performed on the data for the first-format magneto-opticaldisc. RLL (1, 7) processing is performed on the data for thesecond-format magneto-optical disc and the third-format magneto-opticaldisc.

[0084] Moreover, in the recording unit, the interleave, minimumrecording unit, redundancy, address format and the like are switched inaccordance with the thhree types of discs as shown in FIG. 17, thusgenerating recording data.

[0085] Similarly, in the reproducing unit, the decoding processing bythe decoder 10, the demodulation processing by the demodulator 11, theECC processing by the ECC encoder/decoder 14 and the like are switchedin accordance with the three types of discs.

[0086] For example, the reproducing operation when reproducing data fromthe third-format magneto-optical disc will be described. A signal pickedup from the magneto-optical disc 1 is photoelectrically converted in theoptical pickup device 4, then enters the RF amplifier 6, and integratedso as to eliminate the fluctuation of a low-frequency component properto the above-described DWDD. The signal is passed through the LPF fornoise reduction and then quantized by the A/D converter 7. After that,AGC processing and equalization processing are performed and a samplingclock is generated by PLL. Decoding processing based on completion byblock is performed by the decoder 10 and the RLL (1, 7) signal isdemodulated by the demodulator 11. The data stream expanded on thememory unit 13 is processed with RS-LDC processing for each errorconnecting block by the ECC encoder/decoder 14 and is also processedwith descrambling processing and decoding processing by the descramblerand decoder 15, thus being outputted as a DAT1 signal.

[0087] The above-described magneto-optical disc recording/reproducingdevice is applied to a media drive unit 34 and mechanical deck/OPU(optical pickup unit) 35 of a video camera recording/reproducing devicehaving a structure shown in FIG. 9. In FIG. 9, an image signal suppliedvia a camera block 32 from a lens 31 is processed with image processingsuch as motion compensation by a video signal processing unit 33 andthen becomes an MPEG2 data stream. A signal having an OSD signal or thelike added thereto is supplied to an LCD/video/audio/interface block 36and is then monitored on an LCD display 37. The coded MPEG2 data is sentto the media drive 34 and processed as described above as in themagneto-optical disc recording/reproducing device. After that, theprocessed data is supplied to the mechanical deck/OPU 35 and written toa disc. In reproduction, when the disc loaded on the mechanical deck/OPU35 is one of the three types of discs, the light spot shaping deviceprovided in the OPU shapes a light spot corresponding to the disc typeand casts the light spot onto the signal recording surface of the disc.The light spot shaping device can shape an optimum spot for each discsimply by changing an applied voltage pattern to be applied to theliquid crystal unit. Therefore, the compatibility can be securedinexpensively and with a simple structure.

[0088] A magneto-optical disc recording/reproducing device as a secondembodiment of the present invention will now be described. This secondembodiment includes an optical pickup device having another specificexample of the light spot shaping device which has the liquid crystalunit having the split pattern electrode shown in FIG. 3 and the controlunit for changing a voltage to be applied to the split pattern electrodeand thus changing the optical characteristic of a light spot so as toshape the light spot.

[0089] The magneto-optical disc recording/reproducing device of thesecond embodiment is adapted for casing recording/reproducing light to amagneto-optical disc 60 by an optical pickup device 62, thusrecording/reproducing an information signal, as shown in FIG. 10.

[0090] This magneto-optical disc recording/reproducing device has thefollowing elements: an LD 67 provided inside the optical pickup device62 and adapted for emitting a laser beam; an optical system similarlyprovided inside the optical pickup device 62 and adapted for casting thelaser beam emitted from the LD 67 to a signal recording surface of themagneto-optical disc 60 and passing return light reflected from themagneto-optical disc 60; a PD 70 for detecting the return light led bythe optical system; and a light spot shaping device for changing theoptical characteristic of the light spot between when passing therecording light and when passing the reproducing light.

[0091] The optical system is provided in the optical pickup device 62and forms an irradiation path for irradiating the signal recordingsurface of the magneto-optical disc 60 with the laser beam emitted fromthe LD 67 and a return light path for passing the return light reflectedfi-on the magneto-optical disc 60.

[0092] The light spot shaping device has a liquid crystal unit 65provided in the irradiation path of the optical system and having asplit pattern electrode along a radial direction of the optical disc,and a phase compensation liquid crystal driving circuit 76 forcontrolling phase compensation in the liquid crystal unit 65. Thedetails of the structure of the magneto-optical discrecording/reproducing device, including the other parts of thestructure, will be described later.

[0093] The magneto-optical disc recording/reproducing device reproduces,by the above-described domain wall displacement detection, data from themagneto-optical disc (MO disc) 60 on which the data is recorded at ahigh density. First, the principle of the domain wall displacementdetection will be described. The domain wall displacement detectionenables reproduction of data from a magneto-optical disc on which thedata is recorded at a high density, in order to realize high-densityrecording and reproduction on a magneto-optical disc (MO) as a recordingmedium on which rewriting of an information signal is possible. Thisdomain wall displacement detection is a technique of carrying outmagnetic domain enlargement and reading a mark which is smaller than alight spot in reproduction, by using thermal distribution induced by thelight spot. Since the domain wall displacement detection enablescomplete detection of the edge of the mark, it is suitable forreproduction of data from a magneto-optical disc which employs so-called“mark edge recording”.

[0094] A magneto-optical disc for carrying out the domain walldisplacement detection has an enlargement layer 83 and a recording layer81, and also has a switching layer 82 between the enlargement layer 82and the recording layer 81, as shown in FIG. 11. The principle ofreproduction based on the domain wall displacement detection is todetect the presence of a mark by utilizing quick displacement (domainwall displacement 88) of a domain wall 87 of the enlargement layer 83 toa highest temperature portion when the domain wall 87 comes to a frontend 92 of an isothermal area of not lower than the Curie temperatureinduced by a laser beam 86, as shown in FIG. 11.

[0095] The basic principle of the operation of the second embodiment inthe case where the present invention is applied to a DWDD disc will nowbe described. FIG. 11 shows the characteristic of temperaturedistribution T with respect to the position x of a laser spot, and thecharacteristic of energy density a of the domain wall with respect tothe position x of the laser spot. Moreover, FIG. 11 shows thecharacteristic of driving force F(x) of the domain wall displacementwith respect to the position x of the laser spot.

[0096] In the DWDD disc, the driving force F(x) of the domain walldisplacement at the front end part 92, which contributes toreproduction, is proportional to the slope of temperature distributionin a beam traveling direction indicated by an arrow 90. That is, thedriving force F(x) of the domain wall displacement is expressed by

F(x)=−∂σ/∂x=(−∂σ/∂T)*(∂T/∂x)

[0097] in which (∂t/∂x) is the temperature gradient. From this, it isunderstood that the temperature gradient must be increased in order toquickly carry out the domain wall displacement.

[0098] Meanwhile, in carrying out reproduction from the magneto-opticaldisc on the basis of the domain wall displacement detection, as themagneto-optical disc moves in the direction of the arrow 90, the domainwall 87 quickly is displaced to the highest temperature portion alsowhen the domain wall 87 comes to a rear end 91 of the isothermal area.This domain wall displacement at the rear end part 91 is called ghost.

[0099] To restrain the effect of the ghost generated at the rear endpart, it is necessary to reduce the driving force F(x) of the domainwall displacement at the rear end part 91 and bring the domain walldisplacement away from the reproduction field.

[0100] Thus, in the second embodiment, at the time of reproduction, theintensity of the laser beam is switched on the DWDD disc so that thetemperature gradient in the beam traveling direction is raised toincrease the driving force F(x) of the domain wall displacement at thefront end part, which contributes to reproduction, while the gradient atthe rear end part is lowered to restrain the generation of the ghost andreduce its effect. At the time of recording, such switching of theintensity distribution of the laser beam is not carried out because itlowers the writing efficiency.

[0101] The detailed structure and operation of the magneto-optical discrecording/reproducing device will now be described. In FIG. 10, theoptical system of the optical pickup device 62 has the followingelements: a collimating lens 66 for transforming a laser beam emittedfrom the LD 67 to a collimated beam; a beam splitter 64 for splittingthe collimated beam (laser beam) passed through the liquid crystal unit65 of the optical spot shaping device; an objective lens 63 as an outputend of the laser beam; a Wollaston prism 68; and a condenser lens 69.The irradiation path is made up of the collimating lens 66, the beamsplitter 64 and the objective lens 63. The return light path is made upof the objective lens 63, the Wollaston prism 68 and the condenser lens69.

[0102] The driving of the optical pickup device 62 will now bedescribed. The objective lens 63 is supported to be movable in thetracking direction and the focusing direction by a biaxial drivingcircuit 75. Data on the magneto-optical disc 60 is read by moving theoptical pickup device 62 in a radial direction of the magneto-opticaldisc 60. The optical pickup device 62 is supported by a tread mechanism,not shown, and is thus made-movable in the radial direction of themagneto-optical disc 60. A large shift of the reading position is madeby this thread mechanism. As the objective 63 lens is moved in theradial direction of the magneto-optical disc 60 by the biaxial drivingcircuit 75 on the basis of a tracking servo operation, a small shift ofthe reading position is made. Moreover, as the objective lens 63 ismoved in directions toward and away from the magneto-optical disc 60 bythe biaxial driving circuit 75 on the basis of a focusing servooperation, the focusing of the laser beam on the signal recordingsurface of the magneto-optical disc 60 is controlled.

[0103] The emission of a laser beam and the return of the laser beam inthe optical pickup device 62 having the above-described optical systemwill be described hereinafter. A diffused laser beam emitted from the LD67 is transformed to a collimated beam by the collimating lens 66 andpasses through the liquid crystal unit 65 and the beam splitter 64 ofthe light spot shaping device, which will be described later. Afterthat, the laser beam is condensed by the objective lens and cast ontothe magneto-optical disc 60. In this case, the objective lens 63 ismoved in the tracking direction and the focusing direction by thebiaxial driving circuit 75, as described above. The laser beam emittedfrom the optical pickup device 62 may be a laser beam forreproduction/recording. First, it is now assumed that a laser beam forreproduction is cast from the optical pickup device 62.

[0104] Return light reflected by the magneto-optical disc 60 becomesincident oil the beam splitter 64 via the objective lens 63. The beamsplitter 64 leads the return light toward the Wollaston prism 68. TheWollaston prism 68 splits the return light from the magneto-optical disc60 and casts the split light to the PD 70 via the condenser lens 69.

[0105] The ON/OFF operation and the output level of the laser beamoutput from the LD 67 of the optical pickup device 62 are controlled bya laser driving unit, not shown.

[0106] As the PD 70 of the optical pickup device 62, for example, aphotodetector having two quadrisected light receiving areas is used. Onthe basis of a received light quantity signal detected by the PD 70, amatrix unit 72, which will be described later, acquires amagneto-optical signal MO (main) or the like.

[0107] Another structure and operation of the reproducing processingsystem including the above-described light spot shaping device, forprocessing a reproduced signal from the optical pickup device 62, willnow be described. From each light receiving area of the PD 70 of theoptical pickup device 62, a received light quantity signal is outputted,which is caused to be an electric signal corresponding to the quantityof the received return light from the magneto-optical disc 60. Thisreceived light quantity signal is supplied to an I-V converter 71. TheI-V converter 71 carries out current/voltage conversion of the receivedlight quantity signal. Each received light quantity signal caused to bean electric signal by the I-V converter 71 is supplied to the matrixunit 72.

[0108] The matrix unit 72 performs arithmetic processing on eachreceived light quantity signal and thus generates a magneto-opticalsignal MO (main) corresponding to the data recorded on themagneto-optical disc 60. The matrix unit 72 also generates a focusingerror signal FE and a tracking error signal TE. The matrix unit 72 alsogenerates an RF signal.

[0109] The focusing error signal FE and the tracking error signal TEgenerated by the matrix unit 72 are supplied to a phase compensationcircuit 74, which operates as a servo controller. The phase compensationcircuit 74 generates a focusing driving signal based on the focusingerror signal FE and a tracking drilling signal based on the tracking enor signal TE and applies these signals to a focusing coil and a trackingcoil of the biaxial driving circuit 75. Thus, a servo system for causingthe objective lens 63 to converge at a precise focal point with respectto the direction of the recording track is constituted.

[0110] In this magneto-optical disc recording/reproducing device, theread signal MO (main) from the magneto-optical disc, generated by thematrix unit 72, is supplied to a data detecting unit 78 and data isdetected there on the basis of a reproducing clock, which will bedescribed later.

[0111] The RF signal generated by the matrix unit 72 is supplied to asector detecting unit 73 and a recording mark recorded for each sectoris detected there. From the recording mark recorded for each sector,detected by the sector detecting unit 73, a timing generator 79generates a clock signal having a predetermined frequency and suppliesthis clock signal to the data detecting unit 78 and the phasecompensation liquid crystal driving circuit 76 of the light spot shapingdevice.

[0112] The structure and operation of the recording processing systemwill now be described. In the magneto-optical disc recording/reproducingdevice, when a write signal supplied by a host computer or the like, notshown, the encoder encodes the write signal and then supplies theencoded signal to a magnetic head 80 via a magnetic head driving circuit77. The magnetic head 80 generates a magnetic field corresponding to thesupplied write signal and applies this magnetic field to themagneto-optical disc 60. In this case, the optical pickup device 62casts a recording laser beam via the objective lens 63 to the positionon the magneto-optical disc 60 where the modulation magnetic field isapplied by the magnetic head 80.

[0113] The structure and operation of the light spot shaping device inthis magneto-optical disc recording/reproducing device will be describedhereinafter. As described above, the light spot shaping device has theliquid crystal unit 65 provided in the irradiation path of the opticalsystem of the optical pickup device 62 and having the split patternelectrode along the radial direction of the optical disc, and the phasecompensation liquid crystal driving circuit 76 for controlling phasecompensation in the liquid crystal unit 65.

[0114] The liquid crystal unit 65 has split pattern electrodes A, B, C,D and E, as shown in FIG. 3. The phase compensation liquid crystaldriving circuit 76 changes a voltage to be applied to the split patternelectrodes A, B, C, D and E and thus provides aberration to areproducing laser beam so as to shape a light spot on themagneto-optical disc into a linear direction.

[0115] The basic principle of the operation of the second embodiment inthe case where the present invention is applied to a DWDD disc isalready described with reference to FIG. 11. The above-describedprinciple will now be described in detail with reference to FIGS. 12 and13.

[0116] Referring to FIG. 13, front end enlargement and rear endenlargement of a domain wall of an isolation mark 95 in an isothermalarea 101 will be described first. In FIG. 13A, in the isothermal area101 of a beam spot 100 with respect to the isolation mark 95, front endenlargement due to domain wall displacement of the isolation mark 95 ata front end part is generated at a time t1. By this front endenlargement generated at the time t1, a data signal D is acquired asshown in FIG. 13C. However, at a time t2, which is delayed from thefront end enlargement start time t1 by (isothermal area length d÷linearvelocity V1), rear end enlargement due to domain wall displacement ofthe isolation mark 95 at a rear end part is generated as shown in FIG.13B. Therefore, a read signal (MO signal) based on the domain walldisplacement detection contains, in addition to the data signal D, aghost signal G which has the same signal length as the data signal D anda lower level than the data signal D and is delayed from tie data signalD by the above-described amount d/V1. The read signal is a signal suchthat the levels of both the data signal D and the ghost signal G aresuperimposed.

[0117] In the DWDD disc, the driving force F(x) of the domain walldisplacement at the front end part, which contributes to reproduction,is proportional to the slope of temperature distribution in a beamtraveling direction indicated by an arrow 90, as shown in FIG. 11. Fromthis, it is understood that the temperature gradient must be increasedin order to quickly carry out the domain wall displacement. Thus, thepositive side in the beam traveling direction, that is, on the front endenlargement side, the slope of a characteristic with compensationindicated by a solid line can be made steep, as shown in FIG. 12.

[0118] In carrying out reproduction from the magneto-optical disc on thebasis of the domain wall displacement detection, in order to restrainthe effect of the ghost generated at the time t2, it is necessary toreduce the driving force F(x) of the domain wall displacement at therear end part and bring the domain wall displacement away from thereproduction field, as shown in FIG. 13B. Thus, on the negative side ofthe beam traveling direction, that is, on the real end enlargement side,the slope of the characteristic of the solid line can be gentler than acharacteristic indicated by a broken line, as shown in FIG. 2.

[0119] That is, on the DWDD disc, at the time of reproduction, theintensity gradient in the beam traveling direction may be raised and thegradient at the rear end part may be made gentle to increase the drivingforce of the domain wall displacement at the front end pail, whichcontributes to reproduction, and also to restrain the generation of theghost and reduce its effect.

[0120] The phase compensation liquid crystal driving circuit 76 shown inFIG. 10 changes a voltage to be applied to the split pattern electrodesA, B, C, D and E of the liquid crystal unit 65 and provides aberrationto the reproducing laser beam, thus shaping a light spot oil themagneto-optical disc into a linear direction. Specifically, comacorrection is made under such correction conditions as +λ/10 for theelectrodes A and D, −λ/10 for the electrodes B and E, and 0 for theelectrode C, and the collection quantity is controlled. By doing so, thecharacteristic shown in FIG. 12 is acquired. Since the actualtemperature profile of the spot on the magneto-optical disc due toirradiation with the light beam changes in accordance with the linearvelocity and the temperature characteristic of the medium as shown inFIG. 14, the connection quantity is optimized at the initial stage. Itis sequentially controlled in accordance with the optimization of thecorrection quantity of the beam intensity or the optimum correctionquantity based on the linear velocity.

[0121] The beam intensity distribution as described above need not becorrected at the time of recording because it lowers the writingefficiency. Therefore, in the magneto-optical disc recording/reproducingdevice having the structure shown in FIG. 10, beam distribution isswitched between recording and reproduction.

[0122] Thus, since the magneto-optical disc recording/reproducing devicehas the light spot shaping device provided in the optical pickup device62, when reproducing a recorded signal from the magneto-optical disc(DWDD) 60, a ghost signal can be eliminated, which would be generated inaddition to a data signal 110 by the conventional technique as shown inFIG. 15, and it is possible to provide the data signal 110 alone, asshown in FIG. 16.

[0123] As described above, in the magneto-optical discrecording/reproducing device shown in FIG. 10, a reproducing laser beamcan be cast onto a magneto-optical disc while changing the shape of aspot from a single optical pickup device, thus eliminating a ghostsignal and reproducing a data signal with high quality. Moreover, bycasting a recording laser beam without changing the spot shape, thewriting efficiency at the time of recording can be prevented fromlowering.

INDUSTRIAL APPLICABILITY

[0124] In the light spot shaping device and method according to thepresent invention, a voltage to be applied to the split patternelectrode of the liquid crystal means is changed in accordance with thetype of medium and thus changing the optical characteristic of the spotof light cast onto a plurality of types of removable media from the samelight source via the same optical path. Therefore, optimum light spotsfor the plurality of different media can be shaped.

[0125] Moreover, in the light spot shaping device and method accordingto the present invention, a voltage to be applied to the split patternelectrode of the liquid crystal means is changed at the time ofrecording and/or reproduction and thus changing the opticalcharacteristic of the light spot. Therefore, recording light and/orreproducing light can be cast onto an optical disc while changing theshape of the spot from a single optical pickup device.

[0126] The optical pickup device according to the present invention hasthe liquid crystal means provided in the optical system and having thesplit pattern electrode formed along a radial direction of an opticaldisc, and the light spot shaping means for changing a voltage to beapplied to the split pattern electrode of the liquid crystal means forthe type of the optical disc and thus changing the opticalcharacteristic of the light spot. Therefore, light spots adapted to aplurality of optical discs having at least different track pitches canbe cast thereon.

[0127] Moreover, the optical pickup device according to the presentinvention has the liquid crystal means provided in the optical systemand having the split pattern electrode formed along a radial directionof an optical disc, and the light spot shaping means for changing theoptical characteristic of the light spot between when casting arecording light and when casting a reproducing light. Therefore, therecording light and/or the reproducing light can be cast onto theoptical disc while changing the shape of the spot.

[0128] The optical disc device according to the present invention hasthe liquid crystal means provided in the optical system and having thesplit pattern electrode foiled along a radial direction of an opticaldisc, and the light spot shaping means for changing a voltage to beapplied to the split pattern electrode of the liquid crystal means forthe type of the optical disc and thus changing the opticalcharacteristic of the light spot. Therefore, light spots adapted to aplurality of types of optical discs having at least different trackpitches can be formed on the respective optical discs and informationsignals can be reproduced from the respective optical discs.

[0129] Moreover, the optical disc device according to the presentinvention has the liquid crystal means provided in the optical systemand having the split pattern electrode formed along a radial directionof an optical disc, and the light spot shaping means for changing theoptical characteristic of the light spot between when casting arecording light and when casting a reproducing light. Therefore, thelaser beam for recording/reproduction can be cast onto the optical discwhile changing the shape of the spot.

1. A light spot shaping device for shaping a spot of light cast onto aplurality of types of removable media from the same light source throughthe same optical path, in accordance with the type of the medium, thedevice comprising: liquid crystal means having a split pattern electrodeformed along the direction of a recording track of the medium; andcontrol means for changing a voltage to be applied to the split patternelectrode of the liquid crystal means in accordance with the type of themedium and thus changing the optical characteristic of the light spot.2. The light spot shaping device as claimed in claim 1, wherein thecontrol means changes the voltage to be applied to the split patternelectrode of the liquid crystal means in accordance with the type of themedium, thereby providing aberration to the light at least along thedirection of the track.
 3. The light spot shaping device as claimed inclaim 1, wherein the plurality of types of removable media are aplurality of types of removable optical discs having at least differenttrack pitches.
 4. A light spot shaping method for shaping a spot oflight cast onto a plurality of types of removable media from the samelight source through the same optical path, in accordance with the typeof the medium, the method comprising a control step of providing liquidcrystal means having a split pattern electrode formed along thedirection of a recording track of the medium and changing a voltage tobe applied to the split pattern electrode of the liquid crystal means inaccordance with the type of the medium, thus changing the opticalcharacteristic of the light spot.
 5. The light spot shaping method asclaimed in claim 4, wherein at the control step, the voltage to beapplied to the split pattern electrode of the liquid crystal means ischanged in accordance with the type of the medium, thereby providingaberration to the light at least along the direction of the track. 6.The light spot shaping method as claimed in claim 4, wherein theplurality of types of removable media are a plurality of types ofremovable optical discs having at least different track pitches.
 7. Alight spot shaping device for separately shaping an incident laser beamin recording and in reproduction to a spot of light cast onto a mediumfor recording and/or reproducing an information signal, the devicecomprising: liquid crystal means having a split pattern electrode formedalong the direction of a recording track of the medium; and controlmeans for changing a voltage to be applied to the split patternelectrode of the liquid crystal means between the recording and thereproduction and thus changing the optical characteristic of the lightspot.
 8. The light spot shaping device as claimed in claim 7, whereinthe control means changes the voltage to be applied to the split patternelectrode of the liquid crystal means when the information signal fromthe medium, thus providing aberration to the light incident on theliquid crystal means along the direction of the recording track of themedium so as to change the optical characteristic of the light spot. 9.The light spot shaping device as claimed in claim 7, wherein the controlmeans stops the application of the voltage to the split patternelectrode of the liquid crystal means when recording an informationsignal to the medium and thus does not provide aberration to the lightincident on the liquid crystal means.
 10. The light spot shaping deviceas claimed in claim 7, wherein the medium is an optical disc from whicha recorded signal is reproduced by magnetic enlargement due to a domainwall displacement phenomenon.
 11. A light spot shaping method forseparately shaping an incident laser beam in recording and inreproduction to a spot of light cast onto a medium for recording and/orreproducing an information signal, the method comprising a control stepof providing liquid crystal means having a split pattern electrodeformed along the direction of a recording track of the medium andchanging a voltage to be applied to the split pattern electrode of theliquid crystal means between the recording and the reproduction, thuschanging the optical characteristic of the light spot.
 12. The lightspot shaping method as claimed in claim 11, wherein at the control step,the voltage to be applied to the split pattern electrode is changed whenreproducing the information signal from the medium, thus providingaberration to the light incident on the liquid crystal means along thedirection of the recording track of the medium so as to change theoptical characteristic of the light spot.
 13. The light spot shapingmethod as claimed in claim 11, wherein at the control step, theapplication of the voltage to the split pattern electrode of the liquidcrystal means is stopped when recording an information signal to themedium and aberration is not provided to the light incident on theliquid crystal means.
 14. The light spot shaping method as claimed inclaim 11 wherein the medium is an optical disc from which a recordedsignal is reproduced by magnetic enlargement due to a domain walldisplacement phenomenon.
 15. An optical pickup device for forming a spotof light adapted to a plurality of types of removable optical discshaving at least different track pitches, onto the optical disc, thusreading an information signal, the device comprising: a light source foremitting light; an optical system for casting the light emitted from thelight source onto a signal recording surface of the optical disc andpassing return light reflected by the signal recording surface of theoptical disc; photodetection means for detecting the return light passedby the optical system; liquid crystal means provided in the opticalsystem and having a split pattern electrode stacked in a radialdirection of the optical disc; and light spot shaping means for changinga voltage to be applied to the split pattern electrode of the liquidcrystal means for each type of the optical disc and thus changing theoptical characteristic of the light spot.
 16. The optical pickup deviceas claimed in claim 15, wherein the light spot shaping means changes thevoltage to be applied to the split pattern electrode of the liquidcrystal means in accordance with each type of the optical disc, thusproviding aberration to the light at least along the radial direction.17. The optical pickup device as claimed in claim 16, wherein lightspots adapted to a first optical disc with a track pitch of 1.6 μm andgroove recording, a second optical disc with a track pitch of 0.95 μmand land recording, and a third optical disc with a track pitch of notmore than 0.70 μm and land and groove recording, are shaped by the lightspot shaping means.
 18. The optical pickup device as claimed in claim17, wherein with respect to the first optical disc, the light spotshaping means changes the voltage to be applied to the split patternelectrode of the liquid crystal means and thus provides astigmatism inthe radial direction of the optical disc to the light incident on theliquid crystal means.
 19. The optical pickup device as claimed in claim17, wherein with respect to the second optical disc, the light spotshaping means changes the voltage to be applied to the split patternelectrode of the liquid crystal means and thus provides coma in theradial direction of the optical disc to the light incident on the liquidcrystal means.
 20. The optical pickup device as claimed in claim 17,wherein with respect to the third optical disc, the light spot shapingmeans changes the voltage to be applied to the split pattern electrodeof the liquid crystal means and thus provides astigmatism in the radialdirection of the optical disc to the light incident on the liquidcrystal means and defocuses the light spot.
 21. The optical pickupdevice as claimed in claim 20, wherein a recorded signal is reproducedfrom the third optical disc by magnetic enlargement due to a domain walldisplacement phenomenon.
 22. An optical pickup device for castingrecording light and/or reproducing light for recording and/orreproducing an information signal to an optical disc, the devicecomprising: a light source for emitting light; an optical system forcasting the light emitted from the light source onto a signal recordingsurface of the optical disc and passing return light reflected by thesignal recording surface of the optical disc; photodetection means fordetecting the return light passed by the optical system; liquid crystalmeans provided in the optical system and having a split patternelectrode stacked in a radial direction of the optical disc; and lightspot shaping means for changing the optical characteristic of the lightspot between when casting the recording light and when casting thereproducing light.
 23. The optical pickup device as claimed in claim 22,wherein the light spot shaping means changes the voltage to be appliedto the split pattern electrode of the liquid crystal means whenreproducing the information signal from the optical disc, thus providingaberration to the light incident on the liquid crystal means along atangential direction of a track of the optical disc.
 24. The opticalpickup device as claimed in claim 22, wherein the light spot shapingmeans stops the application of the voltage to the split patternelectrode of the liquid crystal means in a recording mode for recordingan information signal to the optical disc and does not provideaberration to the light incident on the liquid crystal means.
 25. Theoptical pickup device as claimed in claim 22, wherein a recorded signalis reproduced from the optical disc by magnetic enlargement due to adomain wall displacement phenomenon.
 26. An optical disc device having areproducing part for forming a spot of light adapted to a plurality oftypes of removable optical discs having at least different trackpitches, onto the optical disc, thus reading an information signal fromeach optical disc, the reproducing part comprising: a light source foremitting light; an optical system for casting the light emitted from thelight source onto a signal recording surface of the optical disc andpassing return light reflected by the signal recording surface of theoptical disc; photodetection means for detecting the return light passedby the optical system; liquid crystal means provided in the opticalsystem and having a split pattern electrode formed along a radialdirection of the optical disc; and light spot shaping means for changinga voltage to be applied to the split pattern electrode of the liquidcrystal means in accordance with the type of the optical disc and thuschanging the optical characteristic of the light spot; the optical discdevice reproducing the information signal on the basis of the quantityof the return light detected by the photodetection means.
 27. Theoptical disc device as claimed in claim 26, wherein the light spotshaping means changes the voltage to be applied to the split patternelectrode of the liquid crystal means in accordance with each type ofthe optical disc, thus providing aberration to the light at least alongthe radial direction.
 28. The optical disc device as claimed in claim27, wherein light spots adapted to a first optical disc with a trackpitch of 1.6 μm and groove recording, a second optical disc with a trackpitch of 0.95 μm and land recording, and a third optical disc with atrack pitch of not more than 0.70 μm and land and groove recording, areshaped by the light spot shaping means.
 29. The optical disc device asclaimed in claim 28, wherein with respect to the first optical disc, thelight spot shaping means changes the voltage to be applied to the splitpattern electrode of the liquid crystal means and thus providesastigmatism in the radial direction of the optical disc to the lightincident on the liquid crystal means.
 30. The optical disc device asclaimed in claim 28, wherein with respect to the second optical disc,the light spot shaping means changes the voltage to be applied to thesplit pattern electrode of the liquid crystal means and thus providescoma in the radial direction of the optical disc to the light incidenton the liquid crystal means.
 31. The optical disc device as claimed inclaim 28, wherein with respect to the third optical disc, the light spotshaping means changes the voltage to be applied to the split patternelectrode of the liquid crystal means and thus provides astigmatism inthe radial direction of the optical disc to the light incident on theliquid crystal means and defocuses the light spot.
 32. The optical discdevice as claimed in claim 31, wherein a recorded signal is reproducedfrom the third optical disc by magnetic enlargement due to a domain walldisplacement phenomenon.
 33. An optical disc device for castingrecording light and/or reproducing light to an optical disc so as torecord and/or reproduce an information signal, the device comprising: alight source for emitting light; an optical system for casting the lightemitted from the light source onto a signal recording surface of theoptical disc and passing return light reflected by the signal recordingsurface of the optical disc; photodetection means for detecting thereturn light passed by the optical system; liquid crystal means providedin the optical system and having a split pattern electrode stacked in aradial direction of the optical disc; and light spot shaping means forchanging the optical characteristic of the light spot between whencasting the recording light and when casting the reproducing light. 34.The optical disc device as claimed in claim 33, wherein the light spotshaping means changes the voltage to be applied to the split patternelectrode of the liquid crystal means when reproducing the informationsignal from the optical disc, thus providing aberration to the lightincident on the liquid crystal means along a tangential direction of atrack of the optical disc.
 35. The optical disc device as claimed inclaim 33, wherein the light spot shaping means stops the application ofthe voltage to the split pattern electrode of the liquid crystal meanswhen recording an information signal to the optical disc and does notprovide aberration to the light incident on the liquid crystal means.36. The optical disc device as claimed in claim 34, wherein a recordedsignal is reproduced from the optical disc by magnetic enlargement dueto a domain wall displacement phenomenon.